Run shrinker-test for JDK 21 CI build (#2570)

The latest R8 version seems to support JDK 21 now.

.github/workflows/build.yml

@@ -15,8 +15,7 @@ jobs:
         include:
           - java: 21
             # Disable Enforcer check which (intentionally) prevents using JDK 21 for building
-            # Exclude 'shrinker-test' module because R8 does not support JDK 21 yet
-            extra-mvn-args: -Denforcer.fail=false --projects '!:shrinker-test'
+            extra-mvn-args: -Denforcer.fail=false
     runs-on: ubuntu-latest
 
     steps:

shrinker-test/pom.xml

@@ -218,7 +218,6 @@
               but it appears that can be ignored -->
             <groupId>com.android.tools</groupId>
             <artifactId>r8</artifactId>
-            <!-- TODO: When updating to a version which supports JDK 21, remove 'shrinker-test' exclusion from build.yml workflow -->
             <version>8.2.33</version>
           </dependency>
         </dependencies>